Odd...
Mine showed up packed well, and seems robust enough; looks to be about give or take 3mm thick, and fits inside my helmet nicely with enough overlap to either trim or account for a means of fastening...
How much did you need to flex it trying to make it fit? even with untold differences between finished sizes and makers, I can't think why it wouldn't give enough without breaking?
Although, it appears that it may just be the plastic; on mine, you can see where the visor has been cut out of a larger shield (probly welding), because there are teeny tiny chips along the edge, which tells me these are not really a "custom" (molded to shape and not cut) item...
I dunno who T-visors is and I don't mean to sound harsh since I like mine, but $$ wise the idea is, yeno, go to HW store, buy a bunch of full face visors at say $5.00 each, cut them out and put 'em up for around $12 apiece on ebay minus shipping...
I suck at math and even I can figure that one out...